Prepare using the STAR method (Situation/Task/Action/Result) and also just be yourself. Try to relax but have command of the key highlights (and lowlights) of your career. Be open, honest and forthcoming about things your not as comfortable with. Ask for questions to be restated if you don't understand them and don't try to BS the interviewer.
Be confident, understand and be knowledgeable about your craft. Be honest.
Help answer questions real people are asking about your company. Your answers will be 100% anonymous.
The person asking the question will be notified of your answer, and it will be posted publicly. Your identity will be kept private